Coloradans voted overwhelmingly in favor of a measure to legalize physician-aided death for terminally ill patients on Tuesday, making the Centennial State the sixth to adopt so-called "Death with Dignity" laws.

The "End-of-Life Options Act," which will allow patients ages 18 and older with a prognosis of six months or less to request self-administered medicine to bring on death, was approved by two-thirds of voters despite opposition from some religious and medical groups. Now, thanks to the "Yes on Colorado End-of-Life Options" campaign, Colorado will join Oregon, California, Vermont, Washington, and Montana, all of which have legalized the practice in some form.

Despite failed measures in a number of states including Massachusetts and Connecticut, support for "Death with Dignity" laws has grown in recent decades as the demand for physician-aided death rises, partly because of an aging population, medical advancements that prolong the death process, and high-profile advocates for the cause, experts say. A yearly Gallup poll shows that nearly 7 in 10 Americans say that a doctor should be allowed to end a patient's life by painless means if the patient requests it, a significant increase from the 35 percent of Americans supporting euthanasia in 1950.

But debate over the issue is far from settled, as demonstrated by opposition to the Colorado measure. Democrats in the state Legislature had attempted to pass legislation allowing for physician-aided death in recent years, but Republicans rejected the initiatives in the split Legislature.

Although opposition to the End-of-Life Options Act, otherwise known as Proposition 106, came primarily from religious groups, the question of whether to legalize medical aid in dying is not necessarily a partisan one, says Margaret Battin, a professor of philosophy and of medical ethics at the University of Utah. Instead, she sees it as an "issue of liberty."

"Up through the 1960s it was culturally taboo to even mention death, even with somebody clearly dying, and there was no sense that people might wish to have a say in how that goes," she tells The Christian Science Monitor.

Now, Dr. Battin says, as the population grows older and medical advances make the process of dying a more prolonged affair, "people begin to see that although we’re encouraged to think of ourselves as free, and be able to shape our own lives and be the architect of our own lives, there's no reason we should lose that at the end."

While a "Death with Dignity" law has existed in Oregon since 1997, several high-profile advocates for legalization have helped to bring the issue into the national spotlight in recent years. Brittany Maynard, the 29-year-old woman diagnosed with a brain tumor who moved from California to Oregon to take advantage of the state’s Death With Dignity law in 2014, was an especially "game-changing advocate." Her story gave "new life to the pro-assisted suicide movements" and prompted a new wave of legislation among state lawmakers, Charles Camosy, an associate professor of theology at Fordham University in New York, told the Monitor at the time.

But support for such laws is far from unanimous. Legislation in Colorado and elsewhere has consistently faced opposition from religious groups, particularly those affiliated with the Roman Catholic Church, whose United States Conference of Catholic Bishops in 2011 called a the practice a "grave offense against love of self, one that also breaks the bonds of love and solidarity with family, friends, and God." The American Medical Association has also spoken out against legalization, arguing that it is "fundamentally incompatible with the physician’s role as healer, would be difficult or impossible to control, and would pose serious societal risks." And disability rights advocates in Colorado expressed concerns that allowing the practice would cause insurance companies to determine that providing medical aid in dying is more cost-effective than lifelong medical care.

Opponents – and even some advocates – worry about how these policies will evolve into the future. Current laws limit the assisted suicide option to terminal patients diagnosed with six months to live, usually after expensive treatments have been exhausted. But a “slippery slope” argument suggests that as the situation evolves over years or decades, people might begin to clamor for assisted suicide for Alzheimer's, Parkinson's, and [early] onset dementia.

These concerns, experts say, highlight the need for sufficient safeguards built into physician-aided death legislation. The Colorado law, like others, has certain requirements, including that the patient must be at least 18 years old, diagnosed with a terminal illness and a prognosis of six months or less as confirmed by two physicians, and be deemed mentally capable by two physicians of making and communicating an informed decision.

Some opponents of the legislation, however, argued that Proposition 106 did not go far enough in its safeguards, as it does not require that a doctor is present at the time of death, does not prevent patients from "doctor shopping," and does not adequately prevent an heir from plotting the death of a relative to reap their inheritance.

Nearly as controversial as the contents of the Colorado measure itself was the language used to describe the act. As elsewhere, proponents for the legislation tended to use terms such as "dying with dignity” and "right to die," where as opponents favored "physician-assisted suicide," as The Denver Post reports.

While such language reflects stances on the issue, it can also shape perceptions, experts say. And adding to the nationwide movement toward legalization is "the growing acceptance that [physician-aided dying] is not assisted suicide," Arthur Svenson, a professor of political science at the University of Redlands in Redlands, Calif., writes in an email to the Monitor, noting that no states that allow the practice include the word "suicide" in their laws.

"Suicide describes a healthy person who chooses death, while [physician-aided dying] describes a terminally ill person who would rather live," he adds.